For a recent client, I needed a node-add form in a custom path. Unfortunately, loading the form there via code (in order to prepopulate the node object) lead to all sorts of FileField errors, and the solution proved to be extraordinarily simple.
One of the great usability features in the Drupal Form API are simple validators, such as #required. Just set it to true, and Drupal takes care of it. However, when in a multistep scenario, simple validators go haywire since moving to a different step validates the form. Normally, you cannot override form errors within your validation hook... but there's a workaround.
Or why the heck is Google bot refusing to look at my site, when everyone else browses through it just fine